Rytidosperma caespitosum_Keir Morse
Photo by Keir Morse

Rytidosperma caespitosum Risk Assessment

Common names: wallabygrass

Rytidosperma caespitosum -- California

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Evaluation Summary
Summary: 
General Evaluation Information
Date of Evaluation: 
September 5, 2016
Evaluation Time (hrs): 
4 Hours
Evaluation Status: 
Completed
Plant Information
Plant Material: 
If the plant is a cultivar, and if the cultivar's behavior differs from its parent's (behavior), explain how: 
Regional Information
Region Name: 
Climate Matching Map
These maps were built using a toolkit created in collaboration between GreenInfo Network, PlantRight, Cal-IPC, and Agricultural Sustainability Institute at UC Davis.
Climate Matching Maps PDF: 
Invasive History and Climate Matching
1. Has the species (or cultivar or variety, if applicable; applies to subsequent "species" questions) become naturalized where it is not native?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
High
Answer / Justification: 
Native to Australia, naturalized in New Zealand and California. Occurs in 3 counties according to Calflora. In California, Rytidosperma caespitosum is abundant along road shoulders and utility corridors on Sweeney Ridge and in fuelbreaks on adjacent SFPUC lands. On Golden Gate NRA lands, we have mapped 29 gross acres, and 1.2 net acres, mostly in linear distributions along roads. There is probably an equal or greater amount on the adjacent SFPUC lands (Eric Wrubel, pers. comm.).
2. Is the species (or cultivar or variety) noted as being naturalized in the US or world in a similar climate?
Yes or No: 
Yes
Points: 
2
Confidence Level: 
High
Answer / Justification: 
Native to Australia, naturalized in New Zealand and California. Question is marked yes because it is naturalized in California.
3. Is the species (or cultivar or variety) noted as being invasive in the U.S. or world?
Yes or No: 
Yes
Points: 
2
Confidence Level: 
High
Answer / Justification: 
R. caespitosum, and the closely related R. penicillatum are effective colonizers after disturbance, and dense populations can inhibit colonization by other perennial grasses and forbs through a buildup of thatch, especially with continued disturbances such as mowing or grazing. These two species are clearly spread by mowing, and can form long, linear populations along transit corridors. They can be spread away from roads and trails by grazing and wildfire (fire fighting activites). I would say that with disturbance, both species can displace native plants and dominate communities through rapid colonization and inhibition. I have not yet seen much evidence of this species colonizing undisturbed native vegetation. However, wildfires are part of the natural disturbance regime where R. caespitosum occurs, and I would expect to see a dramatic expansion of this species following a wildfire, where there is adequate propagule pressure. This is what happened with R. penicillatum at Point Reyes, where it now infests hundreds of acres in the footprint of the Vision Fire, and after a fire at POST Cloverdale Ranch in San Mateo Co. (Eric Wrubel, pers. comm.)
4. Is the species (or cultivar or variety) noted as being invasive in the US or world in a similar climate?
Yes or No: 
Yes
Points: 
3
Confidence Level: 
High
Answer / Justification: 
The answer should be yes, based on observed invasiveness in California at Sweeney Ridge, and in Lusardi Creek Preserve in Southern California (Eric Wrubel). http://www.calflora.org/cgi-bin/noccdetail.cgi?seq_num=po11745 http://www.calflora.org/cgi-bin/noccdetail.cgi?seq_num=cbo29339
5. Are other species of the same genus (or closely related genera) invasive in a similar climate?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
High
Answer / Justification: 
None of the 16 species of Rytidosperma listed in Randall (2012) are classified as invasive. However, recent information indicates that R. penicillatum is invasive in California and is listed on the Cal-IPC inventory. "R. caespitosum, and the closely related R. penicillatum are effective colonizers after disturbance, and dense populations can inhibit colonization by other perennial grasses and forbs through a buildup of thatch, especially with continued disturbances such as mowing or grazing. These two species are clearly spread by mowing, and can form long, linear populations along transit corridors. They can be spread away from roads and trails by grazing and wildfire (fire fighting activites). I would say that with disturbance, both species can displace native plants and dominate communities through rapid colonization and inhibition. I have not yet seen much evidence of this species colonizing undisturbed native vegetation. However, wildfires are part of the natural disturbance regime where R. caespitosum occurs, and I would expect to see a dramatic expansion of this species following a wildfire, where there is adequate propagule pressure. This is what happened with R. penicillatum at Point Reyes, where it now infests hundreds of acres in the footprint of the Vision Fire, and after a fire at POST Cloverdale Ranch in San Mateo Co. (Eric Wrubel, pers. comm.)"
6. Is the species (or cultivar or variety) found predominately in a climate matching the region of concern?
Yes or No: 
Yes
Points: 
2
Confidence Level: 
Medium
Answer / Justification: 
R. caespitosum's native range matches California's climate in part, and is estimated to be a greater than 50% match. California's climate does not match the distribution in Tasmania and New Zealand.
Impact on Native Plants and Animals
7. Does this plant displace native plants and dominate (overtop or smother) the plant community in areas where it has established?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
High
Answer / Justification: 
R. caespitosum, and the closely related R. penicillatum are effective colonizers after disturbance, and dense populations can inhibit colonization by other perennial grasses and forbs through a buildup of thatch, especially with continued disturbances such as mowing or grazing. These two species are clearly spread by mowing, and can form long, linear populations along transit corridors. They can be spread away from roads and trails by grazing and wildfire (fire fighting activites). I would say that with disturbance, both species can displace native plants and dominate communities through rapid colonization and inhibition. I have not yet seen much evidence of this species colonizing undisturbed native vegetation. However, wildfires are part of the natural disturbance regime where R. caespitosum occurs, and I would expect to see a dramatic expansion of this species following a wildfire, where there is adequate propagule pressure. This is what happened with R. penicillatum at Point Reyes, where it now infests hundreds of acres in the footprint of the Vision Fire, and after a fire at POST Cloverdale Ranch in San Mateo Co. (Eric Wrubel, pers. comm.)
8. Is the plant noted as promoting fire and/or changing fire regimes?
Yes or No: 
No
Points: 
0
Confidence Level: 
Medium
Answer / Justification: 
There is no information on whether R. caespitosum promotes or changes fire regimes. However, it was noted by Eric Wrubel, GGNRA, that a closely related species, R. penicillatum, was able to spread after a wildfire.
9. Is the plant a health risk to humans or animals/fish? Has the species been noted as impacting grazing systems?
Yes or No: 
No
Points: 
0
Confidence Level: 
Medium
Answer / Justification: 
R. caespitosum is not poisonous and has not been shown to impact grazing systems. In its native range in Australia it is considered one of the most valuable native pasture grasses.
Reference(s): 
10. Does the plant produce impenetrable thickets, blocking or slowing movement of animals, livestock, or humans?
Yes or No: 
No
Points: 
0
Confidence Level: 
Medium
Answer / Justification: 
R. caespitosum is a perennial grass which grows to 80 cm tall and would not form impenetrable thickets or block movement.
Reference(s): 
Reproductive Strategies
11. Does this species (or cultivar or variety) reproduce and spread vegetatively?
Yes or No: 
No
Points: 
0
Confidence Level: 
Medium
Answer / Justification: 
R. caespitosum is a bunch grass so it would not spread vegetatively.
12. If naturally detached fragments from this plant are capable of producing new plants, is this a common method of reproduction for the plant?
Yes or No: 
No
Points: 
0
Confidence Level: 
Medium
Answer / Justification: 
R. caespitosum is a perennial grass which is thought to spread mostly by seed.
Reference(s): 
13. Does the species (or cultivar or variety) commonly produce viable seed?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
High
Answer / Justification: 
R. caespitosum produces viable seed in its native range, and is also thought to be spreading by seed in California.
Reference(s): 
14. Does this plant produce copious viable seeds each year (> 1000)?
Yes or No: 
Points: 
Confidence Level: 
Answer / Justification: 
Information is available on the seed production by weight of other species of Rytidosperma (formerly Danthonia), but the weight of individual seeds is not included (Lodge 1993). There is no information available on the number of seeds produced per year by R. caespitosum.
15. Is there significant germination (>25%) of seeds the next growing season, with no requirement of an infrequent environmental condition for seeds to germinate (i.e. fire) or long dormancy period?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
High
Answer / Justification: 
In its native range, wildland harvested seed of R. caespitosum has high viability (60-80%).
Reference(s): 
16. Does this plant produce viable seed within the first three years (for an herbaceous species) to five years (for a woody species) after germination?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
High
Answer / Justification: 
Waters (2009) states that the species is a relatively short-lived perennial (perhaps < 2 years), which means the seed would have to be produced in the first year.
Reference(s): 
17. Does this plant continuously produce seed for >3 months each year or does seed production occur more than once a year?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Medium
Answer / Justification: 
In California it flowers from June to July, so it would not be producing seed for 3 months or greater in California (Eric Wrubel pers. comm.). However, in its native range in Australia it flowers opportunistically in response to rainfall. Main flowering in autumn, secondary flowering spring but will also flower periodically throughout the year (Waters 2009).
Dispersal
18. Are the plant’s propagules frequently dispersed long distance (>100 m) by mammals or birds or via domestic animals?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Medium
Answer / Justification: 
R. caespitosum fruits have a high ratio of bristly hairs to seed mass, and clusters of fruits can adhere together and blow in the wind. Below are a couple internet citations referencing wind dispersal for R. caespitosum. From Florabank factsheet for Austrodanthonia caespitosa (=Rytidosperma caespitosum): "Fruit is dispersed by wind or unintentionally by animals" The citation for this reference is Flynn S, Turner RM, Dickie JB (2004) Seed Information Database (Release 7.0, October 2006). (Online database) http://www.kew.org/data/sid/ (Accessed: July 2007). However, I was unable to find information on seed dispersal in the Kew database. http://www.florabank.org.au/lucid/key/species%20navigator/media/html/Aus... A WRA conducted by Future Farm Industries for invasiveness of R. caespitosum in Australia gave a yes answer to wind dispersal, and noted that the species is known to spread downwind of experimental plots. http://www.futurefarmonline.com.au/knowledge-base-1/environmental-weed-r...
19. Are the plant’s propagules frequently dispersed long distance (>100 m) by wind or water?
Yes or No: 
No
Points: 
0
Confidence Level: 
Low
Answer / Justification: 
R. caespitosum lacks a pappus for wind dispersal and seeds are larger than those usually dispersed by wind or water.
Reference(s): 
20. Are the plant’s propagules frequently dispersed via contaminated seed (agriculture or wildflower packets), equipment, vehicles, boats or clothing/shoes?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Low
Answer / Justification: 
The most likely dispersal mechanism of R. caespitosum is by deliberate planting, or by dispersal along roads and trails by vehicles or humans.
Reference(s): 
Evaluation Notes

Victoria: http://vro.agriculture.vic.gov.au/dpi/vro/vrosite.nsf/pages/water_sss_co...

GGNRA Newsletter: https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&...

PlantNet: http://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&nam...

Jepson eFlora: http://ucjeps.berkeley.edu/eflora/eflora_display.php?tid=80883

Correspondence from Eric Wrubel, September 6, 2016 copied below:

Rytidosperma caespitosum is abundant along road shoulders and utility corridors on Sweeney Ridge and in fuelbreaks on adjacent SFPUC lands. On Golden Gate NRA lands, we have mapped 29 gross acres, and 1.2 net acres, mostly in linear distributions along roads. There is probably an equal or greater amount on the adjacent SFPUC lands. I am cc'ing Don Thomas, the SFPUC IPM specialist, who may know more about the distribution on their lands.

R. caespitosum, and the closely related R. penicillatum are effective colonizers after disturbance, and dense populations can inhibit colonization by other perennial grasses and forbs through a buildup of thatch, especially with continued disturbances such as mowing or grazing. These two species are clearly spread by mowing, and can form long, linear populations along transit corridors. They can be spread away from roads and trails by grazing and wildfire (fire fighting activites).

I would say that with disturbance, both species can displace native plants and dominate communities through rapid colonization and inhibition. I have not yet seen much evidence of this species colonizing undisturbed native vegetation. However, wildfires are part of the natural disturbance regime where R. caespitosum occurs, and I would expect to see a dramatic expansion of this species following a wildfire, where there is adequate propagule pressure. This is what happened with R. penicillatum at Point Reyes, where it now infests hundreds of acres in the footprint of the Vision Fire, and after a fire at POST Cloverdale Ranch in San Mateo Co. (http://calphotos.berkeley.edu/cgi/img_query?enlarge=0000+0000+0408+1847 ).

Reviewed by Eric Wrubel.

Total PRE Score

  • < 13 : accept (low risk of invasiveness)
  • 13 - 15 : evaluate further
  • > 15 : reject (high risk of invasiveness)

PRE Score: 
18
Number of questions answered: 
19
Screener Confidence (%): 
67.4
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Evaluation visibility: 
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